This invention relates to a screw for carpentry. A heretofore known screw 1 as shown in FIG. 6, includes a screw-in portion 11 and a straight portion 12. The screw-in portion 11 tapers toward a pointed end. A thread 13 is provided on the portions 11 and 12 for screwing the screw 1 into a wood workpiece.
However, this screw 1 is likely to crack the wood workpiece because it is forced into the workpiece without first cutting bits off the wood.
In light of this fact, the invention of the present invention has introduced a screw, as shown in FIG. 7, which has disclosed on U.S. application Ser. No. 08/922,639 and it has been issued a Notice of Allowability. The screw is made by milling the tapered portion of the screw 1 to have a cutting recessed surface 14. Thus, when the screw is being screwed into the wood workpiece, the recessed surface can cut a hole on the wood, preventing the crack of the wood caused by a forced screw-in as above mentioned. However, the milling process usually has to be performed in another factory having a milling machine. It is very inconvenient because the manufacturers have to transport the screws to another factory. And the threads 13 of the screws 1 might be damaged when a holder for milling process holds the screws.
Moreover, the screw is likely to move away from the central point when it is being screwed into a wood because the cutting recessed surface 14 is arranged on one side. Consequently, when the screw is being screwed into a wood, an unbalance of force is likely to exist, causing relatively much resistance. Also, the bits of wood cut off are relatively big and might impede the screwing in of the screw.